1. Field of the Invention
The present invention relates generally to space transformers for probe cards and more particularly, to a method of manufacturing a space transformer for a probe card.
2. Description of the Related Art
A probe card usually comprises a main circuit board to be electrically connected with signal-transmitting contacts of a testing apparatus directly, arid a space transformer (hereinafter referred to as “ST”) mounted to a bottom surface of the main circuit board. The space transformer is provided at a top surface thereof with a plurality of top contact pads adapted for being electrically connected with the main circuit board, and at a bottom surface thereof with a plurality of bottom contact pads adapted for being connected with a plurality of probe needles, respectively. The space transformer is designed in such a way that the bottom contact pads of the space transformer are arranged having an interval smaller than the interval of the top contact pads of the space transformer, so that the probe needles, which are connected with the bottom contact pads, will be also arranged with a relatively smaller interval and thereby capable of probing small-sized electronic components.
In general, the space transformer for the probe card is made of a multi-layered circuit board. By means of specific internal circuit layout in each layer of the circuit board, the space transformer having different intervals for the top contact pads and the bottom contact pads can be achieved. However, for this type of space transformer composed of a single circuit board with multi-layers, the space transformer usually needs to be made of a circuit board having a big number of layers and a certain large thickness, resulting in difficulty in manufacturing of such space transformer. Besides, this type of space transformer is usually customized made because the pattern of the contact pads of the space transformer needs to conform to the pattern of the contacts of the specific deices under test provided by the customer, resulting in increase of manufacturing cost.
Another type of commercially available space transformer is composed of a first substrate having a relatively larger area and a plurality of second substrates each having a relatively smaller area. The first substrate is provided at a top surface thereof with a plurality of top contact pads having a relatively larger interval, and at a bottom surface thereof with a plurality of bottom contact pads having a relatively smaller interval. Each of the second substrates is provided at a top surface thereof with a plurality of top contact pads corresponding in position to some of the bottom contact pads of the first substrate, and at a bottom surface thereof with a plurality of bottom contact pads having a relatively more smaller interval for being electrically and respectively connected with probe needles. By means of fixedly mounting the second substrates to the bottom surface of the first substrate in a way that the top contact pads of the second substrates are electrically connected to the bottom contact pads of the first substrate, a space transformer having two tiers is made. This type of space transformer can use relatively thinner circuit boards to serve as the first and second substrates, which are relatively easier in manufacturing. Besides, different space transformers for different devices under test can be made with different second substrates with first substrates of same specification, meaning that they can use the same first substrates.
In the aforesaid space transformer composed of a plurality of substrates arranged in two tiers, the second substrates are usually fixed to the first substrate by reflow soldering and the probe needles installed on the second substrates are adapted for probing a plurality of devices under test at the same time, For example, a plurality of die sites on a wafer, which are to be cut into single dies, can be treated as a plurality of devices under test, each of which is to be probed by the probe needles of a respective second substrate. This kind of the space transformer is a so-called multi-DUT (device under test) ST.
However, in the process of reflow soldering, the second substrates are liable to displace from predetermined positions. If the second substrates are indeed displaced from predetermined positions during reflow soldering, a problem that the probe needles on the second substrates may not be aligned with the electric contacts of the devices under test may happen. Besides, in the process of reflow soldering, the second substrates are liable to incline; in this event, the tips of the probe needles on the second substrates may not be located at a horizontal plane. Under these circumstances, it is needed to adjust the positions and flatness of the probe needles by a special adjusting apparatus after the probe needles are installed on the space transformer, resulting in increase of complexity in the probe card manufacturing process.